Digital terrestrial broadcasting standards include a DTMB (Digital Terrestrial Multimedia Broadcast) standard. According to the DTMB standard, it is possible to select one of a modulation method using a single carrier and a modulation method using a multicarrier as a data modulation method.
Hereinafter, transmitting data according to the modulation method using a single carrier is referred to as “single carrier transmission”, and transmitting data according to the modulation method using a multicarrier is referred to as “multicarrier transmission”.
Upon single carrier transmission, data transmission according to the DTMB standard is performed by cyclically transmitting a PN signal and a data signal. Further, upon multicarrier transmission, data transmission is performed by cyclically transmitting data obtained by applying an IFFT (Inverse Fast Fourier Transform) operation to a PN signal and a data signal. A PN signal is a known signal formed with a predetermined data sequence, and is inserted as a guard interval for preventing an interference between data signals.
A reception device which supports the DTMB standard has an equalizer which receives data transmitted by way of single carrier transmission, and an equalizer which receives data transmitted by way of multicarrier transmission.
[Configuration of Single Carrier Equalizer]
FIG. 1 is a view illustrating a configuration of a single carrier equalizer which receives data transmitted by way of single carrier transmission.
A circuit of a previous stage of a single carrier equalizer performs frequency conversion on a received signal and performs processing such as A/D conversion and orthogonal demodulation on an obtained IF signal. An input signal ID(t) obtained by performing each processing is input to a FFE 21. The single carrier equalizer equalizes a time domain signal using the FFE (Feed Forward Equalizer) 21 and a FBE (Feed Back Equalizer) 23.
The FFE 21 has a variable coefficient filter and a coefficient update unit, and performs a convolution operation on the input signal ID(t) and a coefficient using the coefficient obtained by the coefficient update unit. The FFE 21 outputs a signal OD0(t) which indicates a result of the convolution operation, to an adder 22.
The adder 22 generates an equalized signal OD(t)(OD(t)=OD0(t)+OD1(t)) by adding an output signal OD0(t) of the FFE 21 and an output signal OD1(t) of the FBE 23, and outputs the equalized signal. The equalized signal OD(t) output from the adder 22 is output to an outside of the single carrier equalizer, and is supplied to a hard decision unit 24 and a subtractor 25.
The hard decision unit 24 performs hard decision on the equalized signal OD(t) supplied from the adder 22, and outputs a signal OD′(t) which indicates a hard decision result. The signal OD′(t) is supplied to the FBE 23 and a subtractor 25.
The FBE 23 has a variable coefficient filter and a coefficient update unit, and performs a convolution operation on a signal OD′(t) supplied from the hard decision unit 24 and a coefficient using the coefficient obtained by the coefficient update unit. The FBE 23 outputs a signal OD1(t) which indicates a result of the convolution operation. The output signal OD1(t) is supplied to the adder 22, and is used to add to the output signal OD0(t).
The subtractor 25 subtracts the signal OD′(t) which indicates a hard decision result supplied from the hard decision unit 24, from the equalized signal OD(t) supplied from the adder 22, and outputs an error signal ED(t)(ED(t)=OD(t)−OD′(t)). The error signal ED(t) output from the subtractor 25 is supplied to the FFE 21 and the FBE 23.
The coefficient update unit of the FFE 21 performs a LMS operation based on the input signal ID(t) and an error signal ED(t) supplied from the subtractor 25, and updates a coefficient of the FFE 21.
The coefficient update unit of the FBE 23 performs a LMS operation based on the signal OD′(t) which indicates the hard decision result supplied from the hard decision unit 24 and the error signal ED(t) supplied from the subtractor 25, and updates a coefficient of the FBE 23.
Thus, the single carrier equalizer performs a hard decision operation which is an operation of equalizing the input signal ID(t), an operation of an error signal, and an operation of updating coefficients of the variable coefficient filters (the FFE 21 and the FBE 23) using a time domain signal. “(t)” represents that a signal is a time domain signal.
[Configuration of Multicarrier Equalizer]
FIG. 2 is a view illustrating a configuration of a multicarrier equalizer which receives data transmitted by way of multicarrier transmission. The input signal ID(t) is input to the subtractor 11.
The subtractor 11 cancels a PN signal by subtracting from the input signal ID(t) an estimation value PN′(t) of the PN signal supplied from the channel estimation unit 15, and outputs a data signal (ID(t)-PN′(t)) to the FFT operating unit 12.
The FFT operating unit 12 performs an FFT operation on the data signal supplied from the subtractor 11, and outputs a data signal D(f) to a distortion compensation unit 13. A data signal transmitted by way of multicarrier transmission is subjected to the IFFT operation by an apparatus on the transmission side, and the multicarrier equalizer performs the FFT operation on the data signal. The data signal D(f) is a frequency domain signal.
The PN playback unit 14 plays back a PN signal PN(t), and outputs the PN signal PN(t) to the channel estimation unit 15.
The channel estimation unit 15 has a variable coefficient filter and a coefficient update unit, and performs a convolution operation on the PN signal PN(t) played back by the PN playback unit 14 and a coefficient using the coefficient obtained by the coefficient update unit. The channel estimation unit 15 outputs an estimation value PN′(t) of the PN signal calculated by the convolution operation, to the subtractor 11.
The coefficient update unit of the channel estimation unit 15 performs a LMS operation based on the PN signal PN(t) supplied from the PN playback unit 14 and the error signal EP(t) supplied from the subtractor 11, and updates a coefficient of the channel estimation unit 15.
The control unit 16 supplies the coefficient obtained by the coefficient update unit of the channel estimation unit 15, that is, an estimated impulse response h(t), to the FFT operating unit 17.
The FFT operating unit 17 performs an FFT operation on an impulse response signal supplied from the control unit 16, and outputs the impulse response H(f) to the distortion compensation unit 13.
The distortion compensation unit 13 generates the equalized signal OD(f) by compensating for distortion of the data signal D(f) supplied from the FFT operating unit 12 using the impulse response H(f) supplied from the FFT operating unit 17, and outputs the equalized signal OD(f).
The equalized signal OD(f) output from the distortion compensation unit 13 is output to an outside.
Thus, the multicarrier equalizer performs an operation of distortion compensation which is an operation of equalizing the input signal ID(t) using the data from which a PN is canceled and a frequency domain signal obtained by converting the coefficient of the channel estimation unit 15 into the frequency. “(f)” represents that a signal is a frequency domain signal.
Meanwhile, for example, Non-Patent Document 1 discloses single carrier equalization and, for example, Non-Patent Documents 2 and 3 disclose multicarrier equalization.